First off, vinegaroon isn't a magic solution- dip and presto! There's a few things that need to be done that are only learned by doing. Bitone's batch, Particle's batch and my batch are all a little bit different, and we aren't using the same piece of leather. Also, the 'roon gets better as it ages. My 'roon is at least a year old and I've dropped additional metal in the jar from time to time. As it sits, I can dunk a piece of leather, have it turn black inside 2 minutes, and in 15 minutes there's no smell. The 'roon gets better with age, provided you add enough metal to the brew to completely use up the acid. Ever notice how the vinegarroon smells like vinegar? Keep adding metal to completely reduce the acetic acid (vinegar), and you 'use up' all the stuff making the smell. You also need to give it time. Yes it works after two weeks, but there's still too much acetic acid floating in the brew; so....it smells.
Wet forming should be done while it's wet with 'roon. After forming, toss it in an oven to set it. I use a countertop convection oven, set at 140-150 ish, for about 10 minutes. Then I pull the gun/block from the inside and get it somewhere with moving air. You can place a piece of metal, or even a chilled paper towel inside the holster and it will help pick up the 'sweat' on the inside to speed up drying. Be sure to wipe/replace it from time to time. Once the leather dries, it's somewhat difficult to re-wet, short of total submersion....and even that doesn't work that well.
Here's why- The penetration of the ferric acetate into the leather, seems to push the natural oils and waxes to the surface. That's one of the reasons to oil/condition it after 'rooning. Besides turning black, the piece now acts like you've worked a lot of wax into the surface of the leather- it doesn't want to take moisture. This even effects the flesh side of the leather. As far as stitching.....I use waxed linen thread and hand stitch all my stuff. I haven't had any problems with the vinegaroon discoloring it. Though I don't usually use white thread on black leather, either. The stuff you see dripping off/ soaking off into a towel/rag/etc. is basically 'leather juice', that contains some of the tannins that are displaced. The ferric acetate is still reacting with the tannins, so it comes off as slightly black/blue.
NOTE: When wet molding a 'rooned holster, be sure to either (A) use a blue gun, or ( thoroughly protect the gun. With some of the finishes available, you won't likely see any damage, BUT what about the insides, where there's some drips? I've had to move 'add snaps' (or any other metal hardware) to the end of the assembly list because the 'roon will eat them if it gets on them while wet. Unless you just enjoy refinishing a weapon, don't risk it- especially with a blued finish. It WILL eat the blueing right off, and a good hot blueing (or re-blueing) isn't cheap.
Give the brew some time to season, I think you'll like it more when it's aged a bit.